Question

How can you say that a nucleus is small in size but heavy in mass?

Answer 1

Hint: The nucleus is the positively charged region present at the center of an atom. It is composed of two types of subatomic particles which are packed together tightly. The two types of particles are protons, which have a positive electric charge and neutrons, which are neutral.

Complete answer: The mass of protons and that of neutrons is thousands times greater than the mass of an electron. Protons and neutrons have greater mass than many other subatomic particles. As the nucleus is composed of protons and neutrons, the nucleus will be relatively heavier in terms of mass than most subatomic particles. Rutherford's scattering experiment and deflection of lighter particles like electrons on collision with the nucleus shows us that the nucleus is small in size and heavy in mass. The conclusion from Rutherford’s scattering experiment was that most of the alpha particles passed straight without showing any deviation in their path. This is because there is nothing inside to stop the rays in their path. Some of the alpha particles were deflected by small angles which means the positive charge in an atom is not distributed uniformly.

Note:
Rutherford proved that the positively charged particles and most of the mass of an atom is concentrated in a very tiny volume called nucleus which is very heavy in mass. He also proposed that the electrons revolve around the nucleus with very high speeds in circular paths known as orbits.